As the popularity and affordability of computers have increased, so has the number of computer programs available. The computer programs available are diverse, encompassing a wide variety of applications. In addition, the range of users has broadened from the computer programmer of 10 years ago to businesses that use the computer for a variety of tasks including word processing and accounting.
It is well understood from the nature of digital representations of continuous analog forms that some degradation will occur when translating from a continuous representation (such as a typeface prepared manually by a calligrapher) to a discrete digital representation. Programmers and engineers, the original users of computers and viewers of digital typefaces generated by computers (typically on CRT's and computer printers) were not concerned about how the type looked so long as the characters were somewhat readable. However, not only has the viewer of digital type changed but also the requirements with respect to legibility and degradation of type.
As a result, the ability to provide legible digital typefaces has become extremely important for the automation of the printing and typesetting industry as well as for word processor users who require legible, letter quality type. For further information on digital typefaces, see: Bigelow & Day, "Digital Typography", Scientific American, p. 106-119, August, 1983; Karow, Digital Formats For Typefaces, (URW Verlag 1987).
Typically, to produce a digital typeface, the typeface is developed manually, digitized and input into a digital typeface format such as IKARUS. Problems arise because the control points of the character which define the outline of the character do not always coincide to the discrete grid positions corresponding to the resolution of the digital display or printer. As a result, the control points are rounded off to the nearest grid position and parts of characters which originally had the same dimension (for example the widths of the vertical portions of an upper case "I" and "J") now have different dimensions. This method results in the visual degradation of the typeface because the reader does not easily see and recognize the characters with the height and width relationships among the characters changed. Further degradation of the typeface occurs when the size of the characters is globally increased by multiplying the dimensions by a factor, because the inconsistencies in the typeface are also multiplied by that factor.
Another problem arises due to the fact that the thicknesses or heights of characters or portions of characters may be approximately, but not exactly, the same height or width. As the scale of the typeface decreases, the likelihood of distortion increases due to the small differences in height or width. If, for example, the heights of the characters are exactly the same, the scaled version of each of the characters would also be exactly the same. However, if the heights differ by a small value and the display is a low resolution device, the height of one character may be rounded off to one pixel and the height of another character may be rounded off to a different pixel even though the original difference in height may have been less than 0.25 of a pixel. In small scale (low resolution) cases similar to the above example, it is desirable to round the heights of the character to the same pixel in order to maintain the original symmetry and proportions. Thus, the typeface loses the original symmetry and proportion among characters and portions of characters in the typeface again resulting in the visual degradation of the typeface.
To solve these problems, skilled technicians are employed to manually correct any deficiencies in the typeface by reviewing each character and modifying portions of the character which the technician usually perceives to increase the legibility. However, this process is time consuming and costly. There are two primary variables that have to be considered when scaling a digital typeface for display: (1) the different sizes of the font, e.g. 9 point, 10 point or 12 point; and (2) the different resolutions of the display or output device. For each typeface, the manual process must be performed for each possible scale which is equal to the product of the resolution and font size. In addition, the quality of the work is dependent on the skill of the technician. Computer aided processes have been introduced to assist in the manual process. For example there are systems, which display the character and provide a means for the skilled technician to view and modify the character on the display. However, the process of adjustment, what to adjust and how much to adjust is still performed by a skilled technician. U.S. Pat. No. 4,675,830 discloses a method for producing scaling typeface data in which the relative dimensions of the characters are preserved. However, the process disclosed requires not only the input of data which describe the typeface but also control information such as key points of the typeface which are aligned with the grid points and dimensions that are to exist between grid points. This additional input must be generated manually by a skilled technician who develops the control information by visual inspection of the typeface.